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FXUS62 KGSP 050157 AFDGSP

Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 957 PM EDT Sat May 4 2024

SYNOPSIS
A front will remain stalled over the region through the weekend resulting in periodic showers and thunderstorms. A general summertime pattern sets up early next week, which will keep scattered thunderstorm chances around each afternoon. Highs will trend well above normal by Tuesday, remaining well above normal through at least Thursday.

NEAR TERM /THROUGH SUNDAY/
As of 956 PM EDT Saturday: The last band of evening showers is underway, with a focus across the SC Upstate along roughly the I-26 corridor. This is in conjunction with a passing upper shortwave, which is now located over the western half of the CWA Still expect coverage to diminish after midnight as the shortwave exits the area...but isolated showers may linger on and off all night.
The chance of strong storms and heavy, flood-inducing rainfall should taper off sharply after midnight. Lows will be around 10 degrees above normal. At least patchy morning fog will likely be an issue, at least for locations that have received appreciable rainfall this evening.

Scattered convection, numerous across the mountains, will return Sunday afternoon as instability redevelops. An isolated severe storm will be possible as mid level dry air returns and DCAPE values increase with heating. The mid level dry air will decrease PW values limiting the flood threat. That said, isolated heavy rainfall will be possible. Highs should end up a few degrees above normal.

SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/
As of 145 PM EDT Saturday: Short term period will be generally dominated by building mid-level ridge, but with a shortwave embedded in the pattern lifting up from the MS Valley and traversing the area through the period. Meanwhile a strong system will be gearing up over the northern Rockies and push off into the northern Plains to impact us into the extended. We'll see a warming trend Monday into Tuesday afternoon as the ridge builds aloft and surface high off the New England coast slides south toward Bermuda, with moist southerly flow rounding the base into the Southeast. A summerlike pattern will set up as moisture and instability increase Monday, but very little deep-layer shear to work with. Categorical pops pretty much area- wide but highest in the mountains.

Shortwave pushes east on Tuesday and ridging builds in with stronger SW flow aloft. NAM is a little faster with bringing some deep-layer shear in ahead of the next system. Pops are a little lower on Wednesday as moisture is not quite so widespread, but with warmer temperatures (mid 80s in the Piedmont as opposed to lower 80s on Tuesday) instability is a little higher as well, 1500-2000 J/kg so could be looking at isolated strong to potentially severe with some wet microburst potential.

LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/
As of 215 PM EDT Saturday: Active period for the extended as the upper system moving across the northern plains drags a front through the country Wednesday into Thursday. Should see continued low-level WAA Wednesday with temperatures across the Piedmont climbing again into the upper 80s, even flirting with 90 in the Charlotte Metro area. Best pops will be in the mountains closer to the deep-layer shear and moisture, but cannot rule out isolated activity elsewhere.
With the increased heating and better upper dynamics approaching the area, SBCAPEs will climb again from Tuesday, now reaching 2000-2500 J/kg with over 30kt of deep-layer shear across the area, so where we can get a storm going certainly can't rule out isolated severe activity with a very summer-like microburst feel, though there will at least be movement in the storms so expect some organization.

Things get a little more interesting Thursday as the cold front will begin to push into the area. Although the front will be stretched out somewhat rather than just blasting through, strong DPVA combined with the upper jet provide plenty of synoptic lift. It's a little far out for details but at least the GFS is trying to show a decent 850mb jet as well midday Thursday. Timing of the instability surge and juxtaposition with strongest deep-layer shear might be critical, but somewhere in our forecast area we are currently progged to have 2000-2500 J/kg lined up with >50kt deep layer shear, which is impressive. Forecast trends will need to be monitored. SPC's Day 6 outlook is vague on the area but mentions the possibility of needing to introduce an one or more 15% areas for Thursday when guidance comes into better agreement.

Upper shortwave actually begins to approach later on Friday so pops remain in the forecast until then. However, depending on the actual timing of the front itself, cannot rule out an insitu increase in instability right along the front where there would be a local enhancement in deep layer shear, but uncertainty is quite high on when the front would push through. Pops remain high as in line with the blends but timing will likely change in subsequent forecasts.

AVIATION /02Z SUNDAY THROUGH THURSDAY/
At KCLT and elsewhere: A disgusting aviation forecast continues this evening. Overall, coverage of showers and thunderstorms has waned, but much as the short-term guidance predicted, a more coherent band of showers, with some embedded lightning, has developed over the SC Upstate and parts of NC. Poised to affect the Upstate terminals within the first hour or so of the 00z TAF period, this activity will then shift east, arriving at KCLT in some capacity after midnight. Otherwise, widespread IFR ceilings are expected as a modicum of drying aloft permits better low-cloud development than last night. Some improvement is likely after daybreak, to at least MVFR, with some locations perhaps scattering out enough to get some late morning sunshine. Generally S wind through the period, but should be variable between SSW and SE overnight at all the TAF sites. Another round of convection is anticipated Sunday afternoon, first firing up over the NC mountains and then translating east through evening.

Outlook: Enhanced moisture will combine with a weak/stalled front through the middle of next week, resulting in a period of active/mainly diurnal convective weather each day. There will also be the potential for restrictions associated with widespread fog and/or low clouds each morning.

GSP WATCHES/WARNINGS/ADVISORIES
GA...None.
NC...None.
SC...None.

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